Research On Shape And Properties Control Of CMT Arc Additive Remanufacturing 921A Steel

The cold metal transition arc additive manufacturing technology（WAAM-CMT）has the characteristics of high arc productivity,low cost increase,easy production of large parts and low heat input,which is conducive to the continuous printing operation of parts.10Cr Ni3Mo V（921A）is a low alloy structure steel independently developed by our country.Due to its excellent strength,good toughness,good corrosion resistance and other advantages,it is used in the manufacture of key parts of ships.The welding wire is JS590.In this paper,CMT arc was used as the heat source for the re-additive test,to explore the influencing factors of the additive process parameters on the macro size,microstructure,micro-hardness,tensile property,wear resistance and corrosion resistance of single-pass,single-pass straight wall and multipass block,and to reach the following conclusions:（1）In single-layer and single-pass experiments,the size of the heat input affects the macroscopic size of the pass,and the heat input is affected by the welding speed and wire feeding speed.The results show that the welding width,penetration depth and residual height of the pass decrease gradually with the increase of welding speed,which verifies the positive correlation between the spread property of single pass and welding speed.With the increase of wire feeding speed,the penetration width and penetration depth of the pass increase gradually,and the residual height increases and then decreases with the increase of wire feeding speed,which verifies the positive correlation between the spread property of single pass and the wire feeding speed.When the travel speed is 8 mm·s^-1,the wire feeding speed is 7.5 and 8 m·min^-1,the surface of the pass is relatively smooth,which is the best process parameter.（2）The surface of straight wall becomes rougher with the increase of wire feeding speed when printing multi-layer single-channel straight wall.In terms of microstructure,there is no obvious change in the microstructure of matrix,heat-affected zone and remelting zone compared with that of single-pass welding.No martensitic structure is formed in the sedimentary layer,and the ferrite shape changes to the mixture of acicular and massive ferrite,and a small amount of granular bainite is formed.In terms of microhardness,the hardness of the matrix varies from 230-250 HV_0.5 and that of the additive zone varies from 240 to 290HV_0.5.When the wire feeding speed is 7.5m·min^-1,the average tensile strength of X axis and Y axis are 828.7 MPa and 806.2 MPa,respectively,and the elongation is 13.21%and12.50%,respectively,which are both greater than the tensile property of the deposition with the wire feeding speed of 8 m·min^-1.When the wire feeding speed is 7.5m·min^-1,the self-corrosion potential of the top,middle and bottom are-0.9829 V,-0.8726 V and-0.9905 V respectively.Under the condition of the same welding speed,The corrosion resistance of the additive manufactured with wire feed speed of 7.5 m·min^-1 is better than that of the additive manufactured with wire feed speed of 8 m·min-1.When the wire feeding speed is 7.5 m·min^-1,the friction coefficients in the middle and bottom regions are 0.584,0.611 and 0.602,respectively,while when the wire feeding speed is 8 m·min^-1,the friction coefficients in the bottom,middle and bottom regions are about 0.709.It can be concluded that the wear resistance is better when the wire feeding speed is 7.5 m·min^-1.（3）When the welding speed is 8 mm·s^-1 and the wire feeding speed is 7.5 m·min^-1,the printed multi-layer and multi-pass block does not appear obvious collapse phenomenon,and the overall forming quality of the block surface is good.With the increase of the number of sedimentary layers,the phase composition gradually stabilized,the basic phase composition isα-Fe phase,the basic composition of the heat affected zone is coarse martensite and massive ferrite,in the remelting zone and cladding layer,martensite structure gradually decreased or disappeared,and the acicle and massive ferrite gradually increased to become the main phase.The average microhardness is about 235.6 HV_0.5.With the increase of the number of layers,the hardness increases at the position of heat affected zone due to martensitic transformation,and the average hardness is about 323.9 HV_0.5.When reaching the sedimentary layer and above the region,the microstructure gradually regional stability,hardness values presented periodic changes.The average tensile strength of the samples along X,Y,Z axis and at the joint is 708.2 MPa,707.23 MPa,680.77 MPa and 695 MPa,respectively.The elongation along X,Y,Z axis and the joint was 15.46%,15.36%,12.21%and 14.16%,respectively.The fracture mode at all four locations was ductile fracture with a large number of ductile nests.The self-corrosion potential of matrix,upper,middle and bottom are-0.5054 V,-0.4260 V,-0.4494 V and-0.2963 V,respectively.The self-corrosion potential of the bottom is higher than that of the upper,middle and base,indicating that the corrosion trend of materials in the bottom area is small.The average friction coefficients in the upper,middle and lower regions are 0.673,0.721 and 0.706,respectively.With the increase of the number of sedimentary layers,the tribological properties gradually become better.When the number of sedimentary layers is reached,the tribological properties begin to show a downward trend,which is mainly caused by the increase of grain size in the topmost part of the structure.